Diffusion is a type of passive transport which do not require expenditure of cellular energy for the net movement of a substance from a region of high solute concentration to a region of low solute concentration. This is also referred to as the movement of a substance down a concentration gradient.

Diffusion is a passive movement of molecules along their concentration gradient. While osmosis is the diffusion of water molecules through a differentially permeable membrane or semipermeable membrane.

The same conditions of temperature and pressure, the molar mass is proportional to the mass density. Therefore, the rate of diffusion of different gases is inversely proportional to the square root of their mass densities.

Gas exchange is the process that occurs between oxygen and carbon dioxide. Oxygen is passed from the lungs to the bloodstream and carbon dioxide is eliminated from the bloodstream to the lungs. Exchange of Gas takes place in lungs between the alveoli and capillaries which are tiny blood vessels, placed at the walls of alveoli. The rate of diffusion depends on the thickness of the biological membrane which forms the boundary between the external environment and organisms.

Diffusion is a process in which the gaseous molecules spreads due to their kinetic energy and movement of molecules from their higher concentration to their lower concentration. Hence, The correct answer is option B.

Diffusion is the process of spreading of the gaseous molecule according to their kinetic energy. In this process, particles move from an area of high concentration to an area of low concentration. If the perfume is sprayed in one corner of a room, it will be smelt soon after in the opposite corner. Since the perfume molecules are in constant random motion they bump into each other causing some molecules to be occasionally sent hurtling out of the mass. Gradually, the molecules spread out. 

Diffusion is a passive movement of substances from the region of high concentration to the region of low concentration. Diffusion finally stops when the concentration of particles of two regions becomes the same. Diffusion occurs in both liquids and gases and can take place over long distances. Diffusion in gases is much faster than in liquids the diffusion rate of oxygen in the air is 1,00,000 times more than the diffusion rate of oxygen in the water.

Water obeys laws of pressure and diffusion both. Water moves from a region of high concentration or high pressure to a region of low concentration or low pressure.

So the correct answer is 'Both A and B'.

Diffusion finally stops when the concentration of particles of two regions becomes the same diffusion occurs in both liquids and gases and can take place over long distances diffusion in gases are much faster than in liquids the diffusion rate of oxygen in air is $1,00,000$ times more than diffusion rate of oxygen in water.

Diffusion may be defined as the process of movement of gases. liquids or solutes from the region of higher concentration to the regions of lower concentration till the molecules are uniformly distributed throughout the available space dissolved sugars and ions of potassium and sodium can pass through cell surface membranes by diffusion. Waste products such as urea also pass out of the cell through its membrane by cell diffusion helps in exchange of gases during respiration and photosynthesis. It is also responsible for transpiration.

Selective permeability is the membrane's ability to differentiate between the molecules crossing it.

• Simple diffusion can be defined as the process by which solutes particles are moved along the concentration gradient through the semipermeable membrane (cell membrane)
• Eg- water, oxygen, carbon dioxide, ethanol and urea are transported by simple diffusion.
• This type of transport does not require energy for the transport of molecules across the cell membrane. 
• So, the correct answer is 'Simple diffusion'.

Diffusion is more rapid in gas as compared to liquid, this is because gases have more kinetic energy and gas molecules are smaller compared to liquid molecules. When the temperature is raised, this results in the increase of kinetic energy of the molecules and rate of diffusion is also increased.

In facilitated diffusion, molecules diffuse across the plasma membrane with assistance from membrane proteins, such as channels and carriers.
For active transport, as the movement is against the concentration gradient, carriers or pumps are required. Similarly with Na-K pump.
Simple diffusion is just the movement of molecules from a place of higher concentration to lower concentration without any carrier molecules.
Thus, the correct answer is option (B). 

Cell wall is the outer protective layer of a cell. Cellulose is an important constituent of the cell wall. It is made up of carbon, hydrogen and oxygen. It is is selectively permeable, as it allows molecules upto 30-60kD to pass easily without the expenditure of energy and fully permeable to water and proteins molecules.

Osmosis is the movement of solvent through a semi-permeable membrane to a region of higher solute concentration.

Fat-soluble molecules, such as steroids, alcohols, and some vitamins, can dissolve in the lipid portion of the membrane and diffuse in and out the cell. Water soluble molecules can't pass through the hydrophobic portion of the phospholipid layer.

Both active transport and facilitated diffusion are mediated through membrane proteins, here channel proteins allow diffusion of solutes of appropriate size only, so in this size and shape of transport protein changes while simple diffusion does not require proteins for transportation.

Diffusion is the movement of the particles of different substances from the region of their higher concentration, free energy or diffusion pressure to the region of their lower concentration, free energy or diffusion pressure.

Water is passively transported into the roots and then into the xylem. The forces of cohesion and adhesion cause the water molecules to form a column in the xylem. Water moves from the xylem into the mesophyll cells, evaporates from their surfaces and leaves by diffusion through the stomata. The increased solute concentration causes water to move by osmosis from the xylem into the phloem. The positive pressure that is produced pushes water and solutes down the pressure gradient. So, the correct answer is "Osmosis".

Diffusion is a process in which the molecules intermingle due to their kinetic energy and movement of molecules is from higher concentration to lower concentration. During photosynthesis, the plant produces oxygen as a byproduct and hence the concentration of oxygen inside the cell is higher than the outer environment. Plant releases oxygen in external environment through diffusion process.

Aquatic plants lose most of their metabolic wastes by diffusion directly into the water, surrounding them as the concentration of that metabolic wastes is more in the cell as compared to the surroundings. They do not have to store the waste products as terrestrial plants do. Thus, the correct answer is option A.

CO$ _2$ and O$ _2$ are gases so, they move in and out of the cell by diffusion. Diffusion is a process in which the gaseous molecules spreads, due to their kinetic energy and movement of molecules is from higher concentration to lower concentration. 

Diffusion is the movement of water molecules from higher concentration to lower concentration. It also transfers the molecule along the electrochemical potential gradient.

A.In the system A, inward diffusion of water takes place with slow rate

B. In the system B, inward diffusion of water takes place with medium rate.

C.In the system C, inward diffusion of water takes place with maximum rate

D.In the system D, inward diffusion of water takes place with high rate

So, the correct option is ‘System C’.

$O _{2}$ and $CO _{2}$ are exchanged in the alveoli by simple diffusion. The factors that affect the diffusion are pressure gradient of the gases, solubility of the gases and the thickness of the membranes involved in diffusion.